1. Field of the Invention
This invention relates to a liquid injection (ink jet) recording apparatus, and more particularly to a liquid injection recording apparatus in which stability of liquid projection can always be maintained.
2. Description of the Prior Art
Non-impact recording methods have been attracting attention in that the noise produced during recording is negligible. Among them, the ink jet recording methods which are capable of high-speed recording and of recording without requiring a special process such as fixation on plain paper are highly effective methods, and various systems of such methods have heretofore been proposed and apparatuses embodying them have been devised. Some of them have been improved and commercialized and some of them are still being studied in order to be put into practice.
Among them, the methods disclosed, for example, in Japanese Laid-open Patent Application No. 51837/1979 and German Laid-open Patent Application (DOLS) No. 2843064 have a feature different from other ink jet recording methods in that thermal energy is caused to act on ink liquid to thereby provide generative power for forming flying drops of liquid.
That is, in the recording methods disclosed in the aforementioned publications, the liquid subjected to the action of thermal energy undergoes a state change involving a sharp increase in volume including generation of bubbles and, due to the force resulting from such state change, drops of liquid are projected from the discharge port at the end of the recording head which is a major portion of the recording apparatus, and fly and adhere to a recording medium, thus accomplishing recording.
Particularly, the ink jet recording method disclosed in DOLS 2843064 can not only be very effectively applied to the so-called drop-on demand recording method, but also the recording head portion facilities the formation of high-density multi-orifice heads of the full line type and thus, this method has an advantage that images of high resolution and high quality can be obtained at a high speed.
Thus, the above-described ink jet recording method has various advantages, but in order for images of high resolution and high quality to be recorded for a long time or for the service life of the apparatus to be greatly improved, some maintenance system to ensure that drops of liquid are properly projected is an indispensable element. That is, means for eliminating the clogging which may result from the stay of bubbles in the ink jet head, the adherence of ink to the nozzle portion due to evaporation of the ink from discharge ports, or the entry of dust is required. Also, in the aforementioned ink jet recording apparatus using an electrothermal converting element, a thermal action which will bring about the gasified state of ink occurs and therefore, for example, where continuous recording is effected for a very long time, insoluble deposits may be created on the thermally acting surface to clog the discharge ports or the like and thus, means for eliminating such deposits is also required.
Such a maintenance system is an indispensable element for greatly improving the service life in ink jet recording apparatuses using other methods than the method of causing thermal energy to act to thereby project drops of liquid as previously described.
For the solution of such problems, there are known (1) a system whereby the discharge ports are capped and obstacles and ink in the ink supply path are sucked by a suction mechanism, and (2) a system whereby viscosity is regulated by the use of ink and ink solvent. However, these systems have suffered from a problem that the apparatus becomes considerably complicated. For example, in the case of the system (1), the accuracy of the position of the discharge ports and the position of the suction holes disposed in the capping mechanism must be ensured and difficulties, such as manufacturing and assembling the parts of the apparatus with sufficient accuracy, are encountered. In the case of the system (2), an ink tank, a pump and a valve mechanism must be provided discretely from one another and this leads to a more complicated mechanism. A problem common to these two systems is that when recovery of the projection state is to be carried out, ink and obstacles are finally discharged from the discharge ports for discharging the ink, and, for example, where obstacles larger than the discharge ports (dust, deposits, etc.) are present, the obstacles cannot be eliminated by any means.